This invention relates generally to a method for preparing organosilicon amine and amide capped resins and to the organosilicon amine and amide capped resins obtained thereby. More specifically, the method involves the reaction of a silozane resin containing silanol groups with a cyclic silazane to give a silicon-capped siloxane resin containing amino functionality and the reaction of the amino functionality with an acyl halide to yield a siloxane resin with amide organofunctionality.
Aminosilicon compounds are well known in the organosilicon art as exemplified by U.S. Pat. Nos. 2,557,803, 2,738,357, 2,754,312, 2,762,823, 2,998,406, 3,045,036, 3,087,909, 3,355,424, 3,560,543, 3,890,269, 4,036,868, 3,355,424, 4,507,455. The silylation of hydroxyl groups in siloxane resins as an endcapping process also is well known in organic synthesis and occurs effectively with silazanes, silylamines, acetoxysilanes, acetamidosilanes and oximosilanes. However, in none of the methods known for preparing aminosilicon compounds or silylating siloxane hydroxyl groups is a silanol group capped with the silylating moiety while at the same time introducing an amino group into the compound.
Organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals are well known and have been described in U.S. Pat. No. 4,608,270 to Varaprath, which is herein incorporated by reference.
As mentioned in Varaprath U.S. Pat. No. 4,608,270 and as taught in U.S. Pat. No. 2,929,829 to Morehouse, Japan 51/108022 to Furuya et al., Japan 56/74113 to Takamizawa, and West German DE 2365272 to Koetzsch et al., acylaminoorganopolysiloxanes can be synthesized by reacting aminosiloxanes with the corresponding acid chloride in the presence of a tertiary amine such as triethylamine. However, such a synthesis has several disadvantages. First, the removal of the voluminous precipitate of triethylamine hydrochloride by filtration is tedious. Second, a small amount of HCl is liberated even when an excess of amine is used. This HCl is detrimental to the stability of the polymer especially when the acid chloride has other reactive vinyl functionality such as where the acid chloride is an acrylyl chloride.
An alternative method for the preparation for the acylaminoorganopolysiloxanes involves the reaction of aminosiloxanes and silanes with an acid anhydride or ester at elevated temperature. This is taught in U.S. Pat. No. 4,507,455 to Tangney and Ziemelis, assigned to the assignee of the present invention. Unfortunately at the elevated temperatures of the reaction, acrylamide derivatives undergo Michael additional and amidation of the acrylic double bond resulting in unwanted byproducts and crosslinkage of the desired product which ultimately causes the polymer to gel.
Finally as taught in the above-mentioned U.S. Pat. No. 4,608,270 to Varaprath, these problems can be overcome by reacting the aminosilanes and siloxanes with acid chlorides in the presence of aqueous sodium hydroxide. The HCl that is produced on addition of acyl chloride is neutralized by hydroxide in the aqueous phase.